Relationship between molecular weight and clearance (K)
What solutes should be removed is significantly important from the point of view of technological aspect introduced in this chapter.
Small molecular weight (molecular weight less than 1000) are strongly affected by diffusion. Large molecular weights (molecular weight over 5000) are strongly affected by filtration. Solute permeability is affected by membrane pore size (Fig. 5.2).
Relationship between molecular weight and diffusive coefficient.
As reference, diffusive coefficient values are plotted in this figure (Klein et al. 1976, 1979; Colton et al. 1971; Pitts et al. 1978; Holland et al. 1978). Small molecular weight solutes are affected by diffusion, whereas large molecular weight solutes tend to be lower than small molecules.
5.2.1 Dialyzer Performance: Clearance (K)
Clearance (K) can calculate from the blood sample of inlet and outlet dialyzer. In the case of small molecules, blood flow (Q B) is used for K. On the other hand, low molecular weight proteins, such as BMG, calculation K should use plasma flow rate (Q P), because low molecular weight proteins cannot pass through the red blood cell wall. Therefore, K of small molecules is not over the Q B. Low molecules should use not Q B but Q P. As the K is defined by Eq. (5.1),
Dialysis efficiency: Reduction ratio (R) and removal amount (M)
C Bi: inlet of concentration (g/L)
C Bo: outlet of concentration (g/L)
C B(0): concentration at zero minutes (g/L)
C B(t): concentration at t minutes (g/L)
Q Bi: inlet of blood flow rate (mL/min)
Q Bo: outlet of blood flow rate (mL/min)
R and M are strongly affected by patient’s body weight, that is, R becomes higher in patients with small body weight, whereas M becomes higher in patients with large body weight. M also proves to be proportional to the initial concentration in the blood (C B(0)).
Directly comparing M does not make sense because higher M implies larger removal or higher concentration. After that, the ratio of M to C B(0), M/C B(0), was introduced for comparison. In terms of clear space (CS), or the removal space by treatment (Akihiro Yamashita et al. 1982), the patient’s side and dialyzer side both can be evaluated. The dimension of CS is “L.” CS occurs when M/C B(0) shows a body fluid volume at which the concentration of solute of interest becomes zero. CS has been used to evaluate for treatment (Kashiwagi et al. 2013; Nagaoka et al. 2011).
5.3 Solute Removal Characteristics by Dialyzer
There are some materials used as dialyzers, which recently can be of three types, namely, low flux, high flux , and super flux. The solute removal characteristics of these dialyzers are different. When compared, low-flux and super-flux dialyzers are completely different (Fig. 5.3).
Comparison in reduction ratio and clearance between low-flux and super-flux dialysis membrane
R and K of KF-15 (EVAL) and APS-15E (PS) were calculated clinically. KF, low-flux; and APS, super-flux. K was measured for 1 h after the start of HD treatment. Q B and Q D were set at 200 and 500 mL/min, respectively, and Q F was 10 mL/min/m2.
5.4 Kinetic Modeling for Blood Purification in Critical Care
From an in vitro study, solute removal experiment was reported (Mineshima 2015). In continuous hemodialysis (CHD) experiments, the Q D should be required at least twice the Q B for sufficient removal of small molecular substances. In the continuous hemodiafiltration (CHDF) experiments, the Q F is about one-fourth of Q B value, and the Q D should be set up at least twice the Q B value.
5.5 Dialyzer Reuse
To save medical costs, dialyzer reuse is practically universal in all the developing countries of Asia (Prasad and Jha 2015). However, the reuse practice is not standardized. Dialyzer reuse is an efficient cost-saving method that allows the use of more efficient and expensive biocompatible synthetic membranes, thereby providing high-quality dialysis to individuals living in countries with limited medical resources without compromising the safety or effectiveness of the treatment (Dhrolia et al. 2014). There was evidence of a higher relative risk of hospitalization (but not mortality) for dialyzer reuse compared with single-use dialysis (Manns et al. 2002). Chemicals such as sodium hypochlorite, peracetic acid, etc, are used for disinfection.